US2542456A

US2542456A - Standardizing centrifugally separable product

Info

Publication number: US2542456A
Application number: US770586A
Authority: US
Inventors: Donald F Ayres
Original assignee: De Laval Separator Co
Current assignee: De Laval Separator Co
Priority date: 1947-08-26
Filing date: 1947-08-26
Publication date: 1951-02-20
Anticipated expiration: 1968-02-20

Description

Feb. 20, 1951 D. F. AYRES 2,542,456

STANDARDIZING CENTRIFUGALLY SEPARABLE PRODUCT Filed Aug. 26, 1947 3 Sheets-Sheet 1 BLEEDER Lme Puor SsPawm-oR Semmron Feb. 20, 1951 2,542,456

v n. F. AYRES I s'rmnmpxzmc CENTRIF'UGALLY ISEPADRABLE Pizonuc'r Filed Aug. 26, 1947 s sheds-sheet 2 INVE N TOP DONALD 1? Anna 1'7 Feb. 20, 1951 D. F. AYRES 2,542,456

STANDARDIZING CENTRIFUGALLY SEPARABLE PRODUCT Filed Aug. 26, 1947 3 Sheets-Sheet 3 /N vE/v T01? Damqza I Axum BY 8m. Wm! ATT IYEYS Patented Feb. 20, 1951 STANDARDIZING CENTRIFUGALLY SEPARABLE PRODUCT Donald F. Ayres, Poughkeepsie, N. Y., assignor to The De Laval Separator Company, New York, N. Y., a corporation of New Jersey Application August 26, 1947, Serial No. 770,588

17 Claims.

This invention relates to centrifugal separation and has for its object to provide an improved method and apparatus for standardizing the concentration of a constituent of a centrifugally separable product by automatically regulating one of the separating conditions. 1

In the preferred practice of the invention, a part of the centrifugally separated constituent is recentrifuged in a pilot separator, thereby separating it into an eflluent and a more highly concentrated constituent. Light from a source of predetermined intensity is directed through the contents of the pilot centrifuge chamber upon a light sensitive element, preferably in a direction generall parallel to the chamber axis of rotation and in the vicinity of the neutral zone in the chamber. In this way, small changes in the concentration oi the constituent fed to the pilot centrifuge will cause greater changes in the quantity of light transmitted through the contents of the pilot chamber to the light-sensitive element, due to the high concentration of the constituent in the region where the light is transmitted.

The pilot centrifuge is preferably provided with a separating bowl having top and bottom walls of transparent material, the bowl also having a central inlet for the feed and separate outlets at different radii for the separated eflluent and concentrated constituent, respectively. The. light source and the light-sensitive or photo-sensitive element may then be arranged in stationary positions outside the bowl, so that the light is directed uponone of the transparent walls and is emitted from the other wall in passing to the light-sensitive element.

The signals or indications from the photosensitive element may be used to control the rate of feed to a primary centrifuge of the open type having free discharge for both separated constituents. However, when the primary centrifuge is of the "closed type having the discharge of at least one of the constituents opposed by a variable resistance, the photo-sensitive element should be arranged to control the variable resistance in the constituent outlet.

For illustrative purposes, the invention will be described in connection with standardizing the butter fat content of cream, although it is to be understood that the invention may be used as well for treating other products having a centrifugally separable constituent whose concentration is to be standardized.

In dairy practice, the cream is usually standardized to a fat content of approximately a predetermined proportion, depending upon the use for which the cream is intended. This standardizing operation is important because the butter fat is by far the most valuable constituent of the product. Heretofore, it has been common practice to concentrate the cream as closely as possible to the desired fat content by centrifugally separating skim milk from the cream, the centrifugal separator being so adjusted at the outlets for the separated skim milk and cream constituents that the discharged cream will have approximately the desired fat content. It is well known, however, that cream separators of the centrifugal type are sensitive to variations in feed rate, temperature of the feed, and back-pressure at either of the separated constituent outlets. These variations in external conditions often occur in the dairy, and accordingly it is necessary to readjust the centrifugal separator frequently to compensate for them. Such readjustments are objectionable not only because of the demands upon the operator but also because it is not always possible, due to the human element, to obtain in the discharged cream a fat content within the desired limits. Consequently, after the centrz'fugal separating operation, it is often necessary to eil'ect an additional adjustment of the fat content of the cream, as by adding heavier cream or skim-milk, to avoid an insufiiciency or excess of butter fat.

A more specific object of the present invention, therefore, resides in the provision of an improved process by which the centrifugally separated cream is standardized automatically and accuratel within the desired limits, with respect to the fat concentration, and a novel apparatus by which the process can be practiced expeditiously.

According to a preferred form of the invention as applied to the standardizing of cream, the milk or partly concentrated cream is fed to a primary centrifuge of the closed type having the discharge of the cream opposed by a variable resistance, such as a valve, and wherein skim milk is removed and discharged separately from the cream. Part of the discharged cream is then fed to a pilot separator wherein variations of the light-transmitting ability of the cream are determined. This determination is'effected automatically by passing light from a source of predetermined intensity through the cream and upon a light-sensitive element, such as a photo-cell. The light-sensitive element, in turn, is connected to the valve or other variable resistance and operates to vary this resistance in accordance with changes in the amount of light transmitted by the discharged cream to the photo-sensitive element. That is, when the discharged cream passing to the light source has a fat content above the desired proportion, the additional fat globules will reduce the amount of light transmitted to the light-sensitive element, which will cause operation of the variable resistance to decrease the resistance to discharge of cream from the centrifuge, thereby reducing the fat content of the discharged cream. when this fat content becomes too low, a reverse operation is effected. Thus, the fat content of the discharged cream is automatically maintained substantially constant, irrespective of variations in the external conditions affecting the centrifuge.

When it is desired to standardize milk by removing excess cream, the feed to the pilot centrifuge is derived from the standardized milk discharged from the primary centrifuge, rather than from the discharged cream.

For a better understanding of the invention reference may be had to the accompanying drawings, in which Fig. l is a schematic view of a preferred form of the new apparatus, showing in vertical section the pilot centrifuge and light-responsive device for determining variations in the light transmitting ability of the discharged cream;

Fig. 2 is an enlarged vertical sectional view of part of the apparatus illustrated in Fig. 1, showing the valve arrangement for varying the resistance to discharge of the separated cream from the primary centrifuge, and

Fig. 3 is a schematic view of the electrical circuits for adjusting the regulating valve under control of the photo-sensitive element.

The apparatus as illustrated comprises a centrifugal separator 10 which is preferably of the air-tight" type wherein the centrifugal bowl has inlet and outlet connections closed to the atmosphere. The milk or partly concentrated cream is fed to the centrifuge through a supply pipe II, and the skim milk and the standardized cream are discharged separately through outlets i2 and I3, respectively. The cream discharge is provided with a regulating device, shown generally at M, by which the resistance to discharge of the separated cream from the centrifuge bowl may be varied. The regulating devic It may be of the type disclosed in Patent No. 2,145,544 of C. H.

Hapgood, dated January 31, 1939. As shown particularly in Fig. 2, the device H comprises a vertical pipe l5 located on top of the cover for the centrifuge frame, above the skim milk outlet l2. The pipe I! is secured to the frame cover by a threaded ring I B and communicates through a central passage I! in the cover, and through the usual tightening device or seal (not shown), with the cream outlet from the rotating bowl. Interposed between the pipe I! and the passage I1 is a valve seat ll having a centrally depressed portion l8 provided with valve openings it. A valve member in the form of a disc I9 normally engages the top of the seat It and has a central opening through which the reduced end 20 of a stem 2| extends, the lower part of the extension 20 being guided in a central opening in the depressed part of the valve seat. Separated cream from the centrifugal bowl is adapted to flow upwardly through passage l1 and openings II and lift the valve disc l9, due to the discharge pressure of the cream, whereby the latter flows outwardly around the periphery of disc l9 and up through the pipe It, finally passing through the outlet ll.

A flexible diaphragm or membrane 28 is disposed at the upper end of pipe II where it is clamped in position by a superimposed casing 24, the parts 24 and It being held together by a threaded ring 25. The stem 2| fits closely in a central opening in diaphragm 22 and at its upper end engages a plunger 2| slidable in the bottom wall 24' of casing 24. The plunger 2| is urged downwardly by a compression spring 28 coiled around the lower end of a threaded shaft 21, the upper end of the spring engaging a shoulder on the shaft. Thus, the spring acts to depress the plunger, the stem 2| and diaphragm 23, so that the shoulder near the lower end of the stem holds the valve it against its seat with a yielding resistance to the discharge of cream. The shaft 21 extends upwardly through a central opening in a horizontal wall 24 in the casing and through an upwardly extending hollow boss 2M on the horizontal wall. Within the boss 24, the shaft 21 is provided with a vertical groove 21' into which a pin 28 projects from the boss.

The shaft 2! is adjustable vertically in boss 24 by means of a worm wheel 30 having internal threads mating with the external threads at the upper portion of the shaft. The worm wheel 30 is held against the top of boss 24 by a collar 3! surrounding the shaft and interposed between the worm wheel and the closed upper end of casing 24. An extension 21 of the shaft projects upwardly through a central opening in the top of casing 24, for a purpose to be described presently. The worm wheel 30 meshes with a worm 32 mounted on a horizontal shaft 32 extending through the casing wall from a reversible electric motor 34 adapted to be energized from the line conductors II, 35.

It will be understood that when motor ll rotates in one direction, the worm wheel 30 will be driven so as to elevate the shaft 21, which is held against rotation by the pin 28 in groove 21. As a result, the force of spring 26 against plunger 2i and valve disc ID will be reduced, thereby reducing the resistance to discharge of the separated cream constituent from the centrifugal bowl. This, in turn, will cause a larger amount of skim milk to discharge with the cream through outlet ll, so as to reduce the proportion of butter fat in the cream. Conversely, when motor 24 is rotated in the opposite direction, the threaded shaft 21 will be lowered to impose additional compression in spring 26 and thus increase the resistance to discharge through cream valve It, whereby the proportion of butter fat in the cream from outlet is will be increased.

This discharged cream from outlet It passes through a cream line 36 from which a branch bleeder line 3! extends to a pilot centrifuge It. As shown in Fig. 1, the centrifuge 3| comprises a centrifugal bowl 39 made of transparent materiai, such as a plastic. The bowl 3!, which may be formed by molding the plastic, is provided with a separating chamber 40 and an axial spindle ll by which the bowl is supported and rotated in a suitable frame (not shown). A neck 42 projects upwardly from the bowl I9 and has a central inlet passage 42 for receiving the cream from the bleeder line 31, the cream flowing downwardLv through passage 43 and outwardly through passages 44 into the separating chamber. The cream entering chamber 4 0 is centrifugally separated into an outer annulus of skim milk and an inner annulus of cream. Cream from the inlet annulus is constantly discharged from the separating chamber through an outlet 45 leading upwardly through neck 42 to a stationary collecting cover 46 having a discharge spout 46. The separated skim milk is discharged from the outer part of chamber 48 through a passage 41 extending upwardly within the neck 42 to cover 46, from which the skim milk is discharged with the cream through spout 46. The cream discharge may be adjusted by a regulating screw 48 near the discharge end of passage 41.

.The pilot bowl 38 is of the ratio" type designed to allow run ahead of the separated constituents in their discharge from the separating chamber.

Adjacent the bowl 39 is an opaque casing 58 having a horizontal partition dividing the easing into two compartments. In the upper compartment is a light source 5|, which may be an incandescent lamp, from which light passes through a small opening or slit 5| in the casing 58. The light emitted from opening 5| is conducted by a light-transmitting member 52, which may be made of Lucite, or the like, to the wall forming the top of separating chamber 48. A similar light-transmitting member 53 islocated below the bowl 39 in position to receive light transmitted through the separating chamber from the member 52. The light received by member 53 passes through a small opening or slit 53 in the lower part of casing 58 and impinges upon a photo-sensitive element 54, such as a photo-cell, arranged in the lower compartment of the casing. The photo-sensitive element is connected to an electrical control system, indi- I cated generally at 55 in Fig. 1, by wires 56, the

system 55 in turn being connected to the re-- versible electric motor 34 to efiect adjustment of the regu ating device H.

The detai s of, the electrical control system 55 are illustrated in Fig. 3. As there shown, the

wires 56 connect the photo-cell in circuit with the actuating coil 51 of a micro-ammeter 51 having the usual pointer 58. At opposite sides of the pointer 58 are stationary

permanent magnets

59 and 59 which are so arrang d that when the pointer swings in either direction from its central position, due to a variation in the current through wires 56 from the photo-cell, the adjacent magnet will attract armature 58 on the pointer and hold the latter against the magnet. Assume that the pointer 58 swings to the left due to a decrease in the fat content in separating chamber 48 and a consequent increase in the amount of light received by photo-cell 54 (thus increasing the current flowing through wires 56 and the ammeter). The pointer will then be attracted to and held against magnet 59 so as to engage contact 68. As a result, a circuit will be established from one side 35 of the current source through wire 6|, terminal 62, arm 58, contact 68, wire 63, relay 66 and wire 61 to the other side 35 of the current source, so that the relay 66 is connected across the line 35-35. As a result, the relay 66 will operate switch 68 so as to engage the

switch arms

69 and 18 with contacts 1| and 12, respectively. A circuit will then be established from conductor 35 through the lower field winding 34 of the motor, wire 13, contact 12, switch arm 19, wire 14, the rotor 34 of the motor, wire 15, switch arm 10, contact 16, wire 65, switch 64 and the upper field winding 34 to conductor 35, thus causing the motor to drive shaft 33 in the direction for lowering shaft 21 and increasing the proportion of butter fat in the cream discharged through outlet I3.

Simultaneously with the energizing of motor 34, another circuit is established from conductor 35 through wires 6| and 11, contact 1|, switch arm 69,

wires

18 and 88, slow-acting relay 8|, and

wires

82, 83 and 61 to the other conductor 35. After a predetermined time interval (which may be in the order of one-half of a second) following the energizing of relay 8|, the latter closes switch 84-85 so as to energize the reset coil 86 associated with ammeter 51, the reset coil then returning the pointer 58 to its central position against the action of magnet 59. It will be understood that when the pointer 58 is returned to its central position, the contact 68 is disengaged so as to deenergize relay 66, whereupon switch 68 returns to its initial position so as to de-energize the motor 34 and the slowacting relay 8|.

When the fat content of the cream discharged through outlet I3 exceeds the predetermined proportion, the concentration of fat globules in pilot chamber 48 will quickly increase, this condition being manifested by a tendency for the cream" line in chamber 48 to move outwardly toward the separated skim milk constituent. As a result, the amount of light transmitted through chamber 48 from the light source 5| to the photocell 54 will be correspondingly decreased, thereby decreasing the current flowing through wires 56 and ammeter 51. This will cause pointer 58 to swing to the right until it is attracted by and held against the other magnet 59. Thereupon, a circuit will be established from conductor 36 through wire 6|, arm 58, contact 68, wire 63, relay 66, and

wires

83 and 61 to the other conductor 35. Relay 66 will then actuate switch 68 to cause the

switch arms

69 and 18 to engage contacts 1 I and 12, respectively. A circuit will then be established from conductor 35 through the lower field winding 34,

wires

13 and 88, contact 12, arm 18, wire 15, rotor 34, wire 14, arm 18, contact 16, wire 89, switch 64 and the upper field winding 34 to the other conductor 35, thus causing the motor to operate in the reverse direction so as to raise shaft 21 and decrease the proportion of butter fat in the cream discharged through outlet l3. At the same time, another circuit is established from conductor 35 through wires 6| and 11, contact 1|, contact arm 69, wire 88, slow-acting relay 8|, and

wires

82, 83 and 61 to the other conductor 35. After a predetermined time interval, the relay 8| will then close

switch

84, 85 so as to energize the reset coil 86 and return pointer 58 to its central position, as previously described, whereupon relay 66 will be de-energized so as to open the circuits through motor 34 and relay 8|.

Due to the

permanent magnets

59, 59 and the reset coil 86 with its slow-acting relay 8|, the motor 34 will be energized for a predetermined time interval whenever pointer 58 is displaced from its central position in response to an excess or insufiiciency of butter fat in pilot chamber 40. If the control system should have a tendency to hunt," the effective delay produced by slowacting relay 8| may be enhanced by connecting a condenser 81 in parallel with the reset coil 86.

In order to prevent extreme movements of the threaded shaft 21, with consequent damage to the cream valve regulating mechanism, the extension 21 of the shaft is provided'with a cam 98 adapted to actuate plungers 9| and 92 associated with

switches

64 and 64, respectively.

- 7 when the shaft :1 reaches its desired upper limit, the cam it operates plunger 02 to open switch 84' and de-energize the motor ,and

. when the shaft 21 reaches its desired lower limit,

the cam it operates plunger II to open switch 64 and de-energize the motor.

It will be apparent from the foregoing that the method and apparatus of the present invention provide a completely automatic control of the fat content of cream discharged from the primary centrifuge through line it, so that the discharged cream will be standardized to a predetermined fat content within close limits, regardless of variations in the fat content of the feed to the primary separator through supply line II, or other external conditions. By accurately positioning the opening Iifor the light from lam Ii, and by selecting a suitable configuration for the light-transmitting member II, the light may be directed through the pilot separating chamber 40 in a closely confined path located approximately at the "cream line" dividing the separated cream and skim milk constituents within chamber ll. Thus, when the cream line" moves outwardly or inwardly in chamber 40 due to an increase or decrease. respectively, in the fat content in the lines a and 31. the relatively opaque cream constituent will immediately intercept some of the light rays or allow additional light rays to be transmitted, depending upon the direction of movement of the cream line." Instead of limiting the light transmission through chamber 40 to a closely confined path, the opening II and member 52 may be arranged to direct the light through the chamber in a relatively wide path in the vicinity of the "cream line," whereby the light transmitted to photo-cell 64 will represent an average of the light transmitting ability (and therefore the fat content) of a substantial portion of the contents of chamber It. The latter arrangement, that is, scanning a relatively wide path in the vicinity of the cream line, is preferred since it provides a continuously variable control by means of the electrical circuit through the photo-cell and micro-ammeter. The closely confined or pin-point" light circuit, on the other hand, provides a more "on and of! type of control and will operate best with a polarized relay in place of the micro-ammeter. In either case, the pilot centrifuge 3|, by continuously concentrating the butter fat in the standardized cream sample, makes the photo-cell It more sensitive to changes in the fat content of the standardized cream.

In practice, the regulating screw ll of the pilot separator is adjusted for the approximate fat content desired. This adjustment will cause the "cream line" in the pilot centrifuge to be positioned at the approximate center of the scanning area in the bowl at a certain throughput rate of a certain fat content feed to the bowl. Thereafter, the only necessary adjustment by the operator is the adjustment of the current flow in the circuit of the photo-cell and microammeter, and this may be effected by a variable resistance (not shown) in the circuit. By means of the latter adjustment, when the standardized product has the desired fat content, sumcient current will flow through the circuit to position the micro-ammeter pointer at the mid-point of its scale. For example, if the meter scale should read from to microamperes, the current flow should be adjusted to 5 microamperes at the desired fat content. In the following claims, the term "neutral," as applied to the positionof the pointer or movable member of the micro-ammeter or other electromagnetic device. is intended to denote its position at the center or mid-point of its range of movement.

The invention may be used for standardizing not only whole milk and cream but also various milk products, such as cheese mixes, butter, ice cream, condensed milk and evaporated milk. In fact, the invention may be used for standardizing an mixture with respect to the concentration of a centrifugally separable ingredient thereof, where the light-transmitting ability of the mixture varies in accordance with such concentration.

When the invention is to be used for standardizing whole milk, the bleed line 31 to the pilot centrifuge will be connected to the standardized milk discharge line from outlet l2, instead of the cream discharge line 36 carrying the surplus cream. In other words, the bleed line is arranged to convey a sample of whichever discharge (from the primary centrifuge) is to be standardized. For some purposes the regulating device ll, instead of controlling the lighter discharge, may be arranged to control the heavier discharge through outlet II, or to control the feed through pipe II when the primary centrifugal bowl is of the "open" type in which the rate of feed influences the concentration of the cream or other separated constituent. In separating oil from water, for example, with a "balanced column" type of primary centrifugal bowl, part of the unwanted constituent (water discharge) may be piped to the pilot centrifuge; and the regulating device It may be arranged to control the rate of feed through pipe I I, or to control the discharge pressure on the wanted constituent (oil) when the primary bowl is of the hermetic" type.

The pilot centrifuge, of course, may be of any desired construction in which, for a given rate of feed to the pilot bowl, the inner annulus forming the lighter separated constituent in the bowl will expand outwardly as the proportion of the lighter constituent in the feed increases, and will contract inwardly as this proportion decreases, so that the photo-sensitive element will respond to either an increase or a decrease in the concentration of the butter fat or other centrifugally separable constituent in the feed. While I have shown the light source and the photo-cell arranged outside the pilot bowl and stationary, they may be disposed in the bowl chamber so as to rotate therewith (the electrical connections being made through brushes, or the like, on the bowl shaft), in which case it is unnecessary to provide transparent walls for the bowl. Also, instead of directing the light through the pilot chamber parallel to the bowl axis and between the radially displaced outlets for the respective separated constituents, the light source and photo-cell may be arranged so that the light is directed radially through the annulus forming one of the separated constituents in the pilot chamber, whereby radial expansion or contraction of this annulus in response to changes in the concentration of the cream or other feed to the pilot bowl will vary the amount of light transmitted to the photocell. For illustrative purposes, the pilot centrifuge is shown in Fig. 1 as being larger than the primary centrifuge, although it will be understood that the pilot centrifuge will normall be considerably smaller than the primary centrifuge.

I claim:

1. Apparatus for automatically maintaining substantially constant the concentration of the separated constituent discharged from one of the outlets of a centrifugal separator, which comprises a device connected to the separator for regulating the concentration of said last constituent, a pilot centrifuge having a centrifugal separating chamber and a light source for supplying light rays to the chamber, a duct leading to the pilot centrifuge from one of said outlets for conveying at least part of the discharge therefrom to said chamber, a photo-cell coacting with the light source to receive light rays passing through the chamber from said source, the intensity of the light received by said cell from the source being dependent upon the light-transmitting ability of the content of the chamber where the light rays pass, and an operative connection between said cell and the regulating device for actuating the device in accordance with the intensity of the light received by the photocell, whereby said device counteracts changes in said concentration.

2. Apparatus as defined in claim 1, in which the regulating device includ-s a valve in one of said outlets, and a regulating mechanism connected to the valve for varying the position thereof to change the discharge pressure at said last outlet, said operative connection being connected to the valve regulating mechanism.

3. Apparatus as defined in claim 1, in which the regulating device includes a valve in the outlet for the constituent whose concentration is to be maintained substantially constant, and a regulating mechanism connected to the valve for varying the position thereof to change the discharge pressure at said last outlet, said operative connection being connected to the valve regulating mechanism.

4. Apparatus as defined in claim 1, in which said duct leads from the outlet for the constituent whose concentration is to be maintained substantially constant.

5. Apparatus as defined in claim 1, in which said duct leads from the outlet for the constituent whose concentration is to be maintained substantially constant, and in which the regulating device includesa valve in one of the outlets for varying the resistance to discharge therethrough.

6. Apparatus as defined in claim 1, in which the separating chamber of the pilot centrifuge has walls of light-transmitting material, the light source and the photo-cell being located outside said chamber.

'7. Apparatus as defined in claim 1, in which the separatingchamber of the pilot centrifuge has top and bottom walls of light-transmitting material, the light source and the photo-cell being located outside said chamber and arranged, respectively, to deliver light to one of said walls and to receive light from the other wall.

8. Apparatus as defined in claim 1, in which the separating chamber of the pilot centrifuge has top and bottom walls of light-transmitting material, the light source and the photo-cell being located outside said chamber, .a lighttransmitting member extending from the light source'to a point adjacent the outer face of one of said walls, and a light transmitting member extending to the photo-cell from a point adjacent the outer face of the other wall.

9. Apparatus as defined in claim 1, in which said chamber has outlets for separated heavier and lighter constituents, respectively.

10. Apparatus as defined in claim 1, in which said operative connection includes a reversible electric motor connected to the regulating device, an electromagnetic device connected to the photo-cell and having a member movable to one side of a neutral position upon an increase in said light intensity above a predetermined normal intensity, and to the opposite side upon a decrease in said intensity below the predetermined normal, a source of electrical energy, and means under control of said movable member for connecting the source to said motor to drive the same in one direction upon movement of the member to said one side, and for connecting the source to the motor to drive the same in the opposite direction upon movement of the member to said opposite side.

11. Apparatus as defined in claim 1, comprising also means for limiting the movement of the regulating device through said operative connection.

12. Apparatus as defined in claim 1, in which said operative connection includes a reversible electric motor connected to the regulating device, an electromagnetic device connected to the photo-cell and having a member movable to one side of a neutral position upon an increase in said light intensity above a predetermined normal intensity, and to the opposite side upon a decrease in said intensity below the predetermined normal, a source of electrical energy, means under control of said movable member for connecting the source to said motor to drive the same in one direction upon movement of the member to said one side, and for connecting the source to the motor to drive the same in the opposite direction upon movement of the member to said opposite side, and means coacting with said movable member for retaining the same on one side of its neutral position for a predetermined time interval after initial movement of the member to said side.

13. Apparatus as defined in claim 1, in which said operative connection includes a reversible electric motor connected to the regulating device, an electromagnetic device connected to the photo-cell and having a, member movable to one side of a neutral position upon an increase in said light intensity above a predetermined normal intensity, and to the opposite side upon a decrease in said intensity below the predetermined normal, a source of electrical energy, means under control of said movable member for connecting the source to said motor to drive the same in one direction upon movement of the member to said one side, and for connecting the source to the motor to drive the same in the opposite direction upon movement of the member to said opposite side, and limit switches included in said connecting means and operable by the regulating device to disconnect the motor from the source.

14. Apparatus for automatically maintaining substantially constant the concentration of one of the constituents separated in and discharged from a centrifugal separator, which comprises a device connected to the separator for regulating the concentration of said one constituent, a pilot centrifuge having a centrifugal separating chamber, a duct leading to the pilot centrifuge from one of said outlets for conveying at least part of the discharge therefrom to the pilot chamber, said chamber being adapted to separate said part centrifugally into concentric annuli having relatively high and low concentrations, respectively, of said one constituent, the chamber having separate outlets for discharge {mm the respective annuii, means coasting with the pilot centriiuge and responsive to variations in the relative volumes of said annuii in the chamber, and an operative connection between said means and the regulating device for actuating the device to counteract said variations.

15. In combination with a centrifugal separator having two discharge outlets, one for each of the separated constituents, an apparatus for controlling the concentration of one of said constituents, which comprises a device for throttling the discharge of the concentrated constituent, a pilot centrifugal separator, a feed line from said first separator to the pilot separator through which a portion of said discharged concentrated constituent is led, the pilot separator being operable to separate said portion into two components in concentric annuii and having outlets for the continuous discharge of said components, and means, responsive to changes of the zone of division between said annuli, for operating the throttling device to control the amount of said throttling.

16. A method for standardizing the concentration of one of the constituents separated in and discharged from a locu of centrifugal force, which comprises opposing the discharge of one of the constituents with a variable resistance, continuously feeding from said locus to another locus of centrifugal force at least part of the discharged constituent whose concentration is to be standardized, centrifuging said part in the second locus to separate said part into constituents having relatively high and low concentrations, respectively, continuously discharging said last separated constituents from the second locus. passing light at constant intensity through the second locus in a direction generally parallel to the rotation axis thereof and in a region where changes in the relative amounts of said last separated constituents will vary the amount of light transmitted through the second locus, and varying said resistance in accordance with variations in the amount of light transmitted through the second locus.

17. A method as defined in claim 16. in which said variable resistance opposes the discharge of the constituent whose concentration is to be standardized. 1

DONALD I". AYREB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number